This application is entitled to the benefit of and incorporates by reference essential subject matter disclosed in Japanese Patent Application No. 2001-148157 filed May 17, 2001.
1. Field of the Invention
The present invention relates to a rocker arm for an internal combustion engine, and more particularly to a roller-type rocker arm comprising a roller that is in contact with a camshaft in a slidable fashion.
2. Description of the Related Art
In a valve mechanism of an internal combustion engine, a rocker arm connecting to an intake valve or an exhaust valve to increase the lift of the cam of the camshaft is known. Further, there are various friction surfaces surrounding the rocker arm, and a lubrication mechanism described below is employed to lubricate these friction surfaces.
FIG. 3 shows a conventional rocker arm. In the rocker arm 51, one end of the main body of the rocker arm 52 (hereinafter referred to as xe2x80x9cmain bodyxe2x80x9d) is rotatably supported by a rocker shaft 53, and the other end becomes an actuator that presses the shaft-end of the intake valve or exhaust valve (hereinafter referred to as xe2x80x9cvalvexe2x80x9d) 54 downward. A roller 55 is rotatably supported through a roller pin 56 in the middle part of the main body 52 in a longitudinal direction. A cam 58 of a camshaft 57 slides in contact with the roller 55 from above. In this valve mechanism, the cam 58 applies downward force to the roller 55, thereby depressing the main body 52. The valve 54 resists a valve spring (not shown in the drawings) and is lifted up. Note that the actuator comprises an adjustment mechanism consisting of a cap 60 having a ball screw 59 and a spherical seat 60a, and a locking nut 61.
In this construction, friction surfaces exist between a push 72 attached to the main body 52 and the rocker shaft 53, between the roller 55 and the roller pin 56, between the roller 55 and the cam 58, between the ball screw 59 and the spherical seat 60a, and between the cap 60 and the shaft-end surface 54a. Accordingly, a lubrication mechanism is employed to lubricate these friction surfaces.
In other words, lubricating oil sent from the engine""s oil pump flows through a shaft hole 62 inside the rocker shaft 53, and this oil is supplied to the friction surfaces between the push 72 and the rocker shaft 53 by an oil hole 63 that branches off in a radial direction. Subsequently, the oil is guided from an oil hole 64 inside the main body 52 to an oil passage 65 inside the roller pin 56. Since the exit of the oil passage 65 opens to the external circumference of the roller pin 56, the area between the roller 55 and the roller pin 56 is lubricated. Additionally, the oil is transmitted to both surfaces of the roller 55 by a centrifugal force, and is sprayed in an external radial direction, thereby lubricating the area between the roller 55 and the cam 58. Further, the oil sprayed from the cam 58 by the centrifugal force reaches between the ball screw 59 and the spherical seat 60a, and between the cap 60 and the shaft-end surface 54a, thereby lubricating the friction surfaces.
As shown in FIG. 4, the roller insertion part of the main body 52 is an opening 66 that runs above and below. Reference numerals 67 and 68 depict the push insertion hole and the roller pin insertion hole respectively. The roller pin 56 is constituted as shown in FIGS. 5a-5c and is fixed by pressure in the roller pin insertion hole 68. The oil passage 65 consists of a first hole 69 connected to the oil hole 64 of the main body 52, a second hole 70 extending downward from the first hole 69 axially at a slope, and a taper hole 71 formed to open into the middle part of the pin, which constitutes the exit of the second hole 70 and the oil passage 65. The oil flowing out of the taper hole 71 lubricates the area between the roller 55 and the roller pin 56.
However, when the engine stops, oil flows down from the moving valves, including the rocker arm, to the oil gallery. On the other hand, when the engine starts up, it takes time for the oil to flow up from the oil gallery to the shaft hole 62 in the rocker shaft 53. Even more time is required until the oil reaches each sliding part described above. This is even more so if the oil temperature is low when the engine starts up. Accordingly, when the engine is started up under low temperature conditions after a long period of shutdown, sliding occurs without lubrication for a comparatively long period of time, and there is the possibility of causing abnormal wear, particularly of the roller pin 56, the roller 55, the cam 58 and the valve shaft-end surface 54a. 
Therefore, the present invention was designed with the foregoing problems in view, and it is an object of the present invention to prevent abnormal wear of the friction surfaces surrounding the rocker arm, while also improving reliability by preventing poor lubrication under conditions which are disadvantageous to lubrication, such as when an engine is started up at low temperature after a long period of shutdown.
A rocker arm for an internal combustion engine according to the present invention comprises a bag-shaped oil sump opening upward in the rocker arm main body, and an oil supply port and oil exhaust to conduct the supply and discharge of oil to and from the oil sump as well as control the oil level height of the oil sump. A roller is rotatably provided inside the oil sump and the bottom end of this roller is positioned lower than the oil level height so that at least the bottom end of the roller will be immersed in the oil in the oil sump.
Therefore, when the engine is stopped, the oil in the oil sump adheres to the roller, so that when the engine is started up again, until the time that the oil rises up, the oil adhering to the roller is used and the area between the roller and the cam can be lubricated. In addition, due to the rotation between the roller and the cam, oil can be sprayed onto other friction surfaces. Accordingly, poor lubrication can be prevented even when starting the engine up at low temperature after a long period of shutdown.
Here the roller is mounted to the rocker arm main body and is rotatably supported by a roller pin inserted into the centre of the roller, and it is desirable that the bottom end of this roller pin is positioned lower than the oil level height so that at least the bottom end of the roller pin will be immersed in the oil in the oil sump.
Therefore, when the engine is stopped, the oil in the oil sump is able to adhere to the sliding part between the roller and the roller pin as well, and the problem of poor lubrication can be further eliminated.
It is desirable that the oil supply port is formed so as to penetrate the rocker arm main body, and comprises an entry hole to guide the oil from the shaft passage inside the rocker shaft to the oil sump. It is desirable that the oil exhaust is formed so as to penetrate the rocker arm main body, and consists of an exit hole to supply oil from the oil sump by spraying it near the valve shaft-end.
Therefore, the oil supply port and oil exhaust can be drilled and the drilling process can be conducted with greater ease and at less cost. Further, abnormal wear of the valve shaft-end surface can be prevented, since oil from the oil sump is supplied by spraying near the valve shaft-end.
Further, the valve mechanism of an internal combustion engine according to the present invention is a valve mechanism of an internal combustion engine, which comprises a rocker arm main body, of which one end is rotatably supported by the engine""s rocker shaft, and the other end forms an actuator to press the shaft-end of the intake valve or exhaust valve downward, and a roller rotatably supported by a roller pin in the middle part of the rocker arm main body, a camshaft being in contact with the roller from above in a slidable fashion,
wherein a shaft passage is formed inside the rocker shaft, so that lubricating oil is supplied from the engine""s oil pump through this shaft passage, and a bag-shaped oil sump is defined in the rocker arm main body, so as to contain the roller and roller pin and to open upwards;
the rocker arm main body is provided with an entry hole to guide oil from said shaft passage into the oil sump, and an exit hole to supply oil from said oil sump by spraying near the shaft-end of an intake valve or exhaust valve, formed in said rocker arm main body; and
wherein the oil level height of said oil sump is controlled by the height of the openings of the entry hole and the exit hole into the oil sump, and the height of the bottom end of the roller pin is lower than the oil level height so that at least the bottom end of the roller and roller pin is immersed in the oil in the oil sump.
It is desirable that the entry hole is selectively connected to the shaft passage when the rocker arm main body is oscillating downward. This is so that oil expenditure is optimized and oil is not expended wastefully.